An eco-friendly vehicle is equipped with an electric motor for driving the vehicle using electric power from a high-voltage battery. The main components of the driving motor for producing output are a permanent magnet, a core, and a coil. Electric resistance and magnetic resistance are generated in these components due to electric current or magnetic force applied thereto, which causes heat generation in the motor. Therefore, in a high-temperature condition above a predetermined temperature, irreversible deterioration in performance of the components may occur, which may cause damage to the components and degradation of the performance of the motor. Accordingly, in order to maintain the performance of the motor, cooling for maintaining the temperature of the motor at a certain level is essential.
For this reason, protection logic for protecting the internal components is applied, such that when the temperature of the motor rises above a predetermined level the output of the motor is limited or stopped. If the motor is cooled and the temperature thereof is maintained at a low level, the motor driving time is increased, which results in improved fuel efficiency and driving efficiency of the eco-friendly vehicle.
As methods of cooling a motor, an air-cooling method and a water-cooling method are employed. In the air-cooling method, a heat sink is formed at a motor housing in order to achieve cooling using external cooling air. In the water-cooling method, cooling channels are formed in the interior of a motor housing, or outside a stator, in order to achieve cooling using cooling water.
FIG. 1 illustrates an exemplary air-cooling method. As shown in the drawing, a heat sink 4 is formed at a motor housing 1, which is disposed at the exterior of a rotor 3 and a stator 2. Because it has an indirect-cooling structure such that cooling is performed with respect to the motor housing, rather than to a heat source, the cooling performance is degraded. Therefore, the air-cooling method shown in FIG. 1 has a limitation in cooling performance when the output of a motor is high and a heating value is thus relatively high. Further, because traveling wind of a vehicle is typically used as external cooling air, the air-cooling method has a problem in that it is impossible to control the flow rate of the cooling air depending on the temperature of the motor.
Meanwhile, the water-cooling method is an indirect-cooling method using a heat conduction phenomenon between cooling water, a housing, and a heat source. A driving motor having a water cooling structure is disclosed in Korean Patent Publication No. 2016-0056351 (May 20, 2016). However, the indirect-cooling driving motor, which has a water-cooling structure, has a disadvantage in that cooling efficiency is degraded due to the contact state (i.e. contact thermal resistance) between the components.
For this reason, a direct motor cooling method using oil spray has been recently employed. However, this cooling method has some structural constraints, for example, pertaining to the design of an oil spray hole and oil supply pipe lines, and has a limitation in that only an outer surface of an end coil portion is mainly cooled.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the related art already known to a person of ordinary skill in the art.